Aqueous extract of Bruguiera gymnorrhiza leaves protects against dextran sulfate sodium induced ulcerative colitis in mice via suppressing NF-κB activation and modulating intestinal microbiota

Abstract

Ethnopharmacological relevance

Ulcerative colitis (UC) is tightly associated with inflammation response and oxidative stress. As a folk medicine applied in treatment of diarrhea, Bruguiera gymnorrhiza also possesses anti-inflammatory and anti-oxidative activities, which indicated that B. gymnorrhiza may exert anti-colitis effect.

Aim of the study

To investigate effect and mechanism of B. gymnorrhiza on experimental UC.

Materials and methods

Aqueous extract of B. gymnorrhiza leaves (ABL) was used for investigation in the present study. Murine UC was established through access to 3% dextran sulfate sodium (DSS) for 7 days. Meanwhile, mice accepted treatment with ABL (25, 50, 100 mg/kg) or sulfasalazine (200 mg/kg) once daily. On the last day, disease activity index (DAI) including body weight loss, fecal character and degree of bloody diarrhea was evaluated, colon segments were obtained for length measurement and further analysis and feces were collected for intestinal microbiota analysis.

Results

ABL ameliorated DAI scores, colon length shortening and histopathological damage in DSS-induced colitis mice obviously. SOD activity, levels of MDA and GSH altered by colitis were restored remarkably after ABL treatment. ABL inhibited increases in levels of colonic COX-2, iNOS, TNF-α, IL-6, IL-1β, IL-4, IL-10 and IL-11 in colitis mice. Moreover, ABL prominently suppressed NF-κB p65 and IκB phosphorylation and down-regulated mRNA levels of COX-2, iNOS, TNF-α, IL-6 and IL-1β elevated by colitis. As shown in microbiota analysis, ABL modulated composition of intestinal microbiota of colitis mice.

Conclusion

ABL exhibited protective effect against DSS-induced ulcerative colitis through suppressing NF-κB activation and modulating intestinal microbiota.

Introduction

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder located in the gastrointestinal tract, principally consisting of Crohn's disease (CD) and ulcerative colitis (UC) (Kaser et al., 2010). It is featured as a recurrent and persistent disease bothering sufferers' daily life (Sartor, 2006). Prevalence of IBD in newly industrialized countries is climbing sharply these years following its widespread occurrence in western countries, which is predicted to develop into a global problem in 2025 (Kaplan and Ng, 2017). Distinguished from CD, UC only occurs in colonic mucosa rather than the whole alimentary tract (Engel et al., 2012). To date, the exact pathogenesis of UC remains unclear. The factors triggering UC vary from environment to genetics, gut microbiota and so on (Ananthakrishnan, 2015). Inflammatory cytokines and reactive oxygen species play a critical role in pathogenesis of UC (Pavlick et al., 2002; Neurath, 2014). Studies have reported that occurrence of UC also has close relation to activation of nuclear factor kappa-B (NF-κB) as well (Atreya et al., 2008). Additionally, gut microbiota dysbiosis and metabolic disorders can be observed in UC patients (Lin and Zhang, 2017). Currently, anti-inflammatory drugs, immunosuppressants, biologic therapies against tumor necrosis factor alpha (TNF-α) and combined medication have been commonly applied in the treatment of UC in clinic (Neurath, 2017). However, the status quo of UC treatment is far from satisfaction due to side effects and high expense (Engel and Neurath, 2010). For instance, anti-inflammatory drugs like aminosalicylates can cause headache, diarrhea, allergic reactions, nephrotoxicity and reproductive toxicity in spite of their effectiveness (Pithadia and Jain, 2011). It is urgently to seek for alternative agents for UC treatment.

Bruguiera gymnorrhiza (L.) Lam. is a specie of true mangrove plant belonging to Rhizophoraceae. Apart from environmental protection, it is suggested that mangrove plants may possess a great potential for disease treatment (Lopez et al., 2018). Importantly, B. gymnorrhiza has been applied as a folk medicine in treating diarrhea and recorded in Chinese monographs on materia medica (Huang et al., 2001; Guan et al., 2009). Recent studies have also demonstrated that B. gymnorrhiza leaves were able to prevent diarrhea (Ahmed et al., 2007). Furthermore, B. gymnorrhiza leaves could exert anti-oxidative effect through suppressing production of lipid peroxides and elevating glutathione (GSH) level (Sur et al., 2016). Flavone and sulfur compounds isolated from B. gymnorrhiza were found to inhibit cyclooxygenase-2 (COX-2) enzyme activity and NF-κB activation in vitro (Homhual et al., 2006; Barik et al., 2016). Given anti-diarrheal, anti-oxidative and anti-inflammatory abilities of B. gymnorrhiza leaves, we come up with a supposition that B. gymnorrhiza leaves are likely to have protective effect against UC.

In the present study, we attempt to study potency and mechanisms of aqueous extract of B. gymnorrhiza leaves (ABL) on dextran sulfate sodium (DSS) induced UC in mice. Preliminarily, disease activity index, colon length and histological changes were investigated for anti-colitis effect evaluation. In further, levels of myeloperoxidase (MPO), COX-2, inducible nitric oxide synthase (iNOS), relative oxidative stress markers including superoxide dismutase (SOD), malondialdehyde (MDA), GSH, inflammatory cytokines involving TNF-α, interleukin (IL)-6, IL-1β, IL-4, IL-10, IL-11 were also detected. Additionally, western blot test, real-time PCR analysis and gut microbiota profiling were conducted for mechanism investigation on NF-κB signaling pathway and intestinal microflora.